The present invention relates to a method for shifting in vehicles with a hybrid powertrain, a hybrid powertrain and a vehicle comprising such a hybrid powertrain.
A hybrid-driven vehicle is operated by a combustion engine and an electric machine, which interact to deliver a desired output and to, among others, achieve a good fuel economy in the vehicle. The electric machine may also be used to brake the vehicle, wherein the electric machine functions as a generator and thus returns energy to an electric accumulator in the vehicle. The vehicle is also equipped with a gearbox to distribute power from the combustion engine and the electric machine, and to achieve a suitable gear ratio for the vehicle's driving wheels.
In automated manual transmissions (AMT) with a single input shaft, shifting is carried out by disconnecting the combustion engine from the input shaft and bringing the gearbox into a substantially zero torque state, disengaging the current gear, synchronizing the input shaft and a lay shaft to the next gear, engaging the next gear and subsequently adding a torque on the input shaft by connecting and accelerating the combustion engine and/or accelerating the electric machine. Such a transmission may also comprise a split gear unit between the input shaft and the lay shaft.
When an automated manual transmission is included in a hybrid powertrain, the split gear unit is shifted first, synchronizing the lay shaft's speed with the input shaft's speed via the split gear unit, so that it corresponds to the next gear ratio, and subsequently, with the help of the electric machine, synchronizing the input shaft's and the lay shaft's speed with the speed corresponding to the next gear of a main shaft. Doing this sequentially entails an undesirably long time to complete the shifting, which entails that the vehicle's speed may be reduced unwittingly, which thus requires more energy and an increased fuel consumption to accelerate the vehicle to a desired speed.
DE102011080849 shows how the shifting time may be shortened by simultaneously shifting a main gearbox and a range gearbox.
DE102009000710 shows a transmission equipped with a braking device and an electric motor to control the shifting.